Control system



Oct. 4, 1949. J. L. BARKER CONTROL SYSTEM Filed Dec. 21, 1944 r w N m z m M m m m B v m 5m Patented Oct. 4, 1949 CONTROL SYSTEM John .L. Barker, Norwalk, Conn, asslgnor, by

mesneassignments, to Eastern Industries, Incorporated, a corporation of Delaware Application December 21, 1944, Serial No. 569,191

' 21* Claims.

Thisinvention relatesto a control system for ing .devices or indicating .devices and the like. In

.aparticular application, the invention relates to a system for counting thev passage of objects over or .along a trafilcarteryand for insuringan accurate countincircumstances, for example, wherein a vehicle: may haltv and. momentarily reverse vwhile itnisnupon or within thezone of the actuatin means for the counting device. I

Controlsystems accordance with the invention areespecially useful in-providing an accurate 'scou-nt of 'road vehicle trafiic, ortraflic at toll bridges, tunnels, or highways, or wherever it is desired toaoperate one counter for recording vehicles passing in :a forward direction and another counterijor vehicles passingin the reverse direction. t'In; such installations, the: operation of the system is advantageously initiated by a multicontacttreadle-:placed in the roadway, for, actuation :hYflVBhiClB wheel rolling .over .the contacts in. sequence. Itis desired to have the counting .of-rvehicle axles as accurate .aspossible andwsub- :stsmtia-lly proof against actuationby pedestrians lor tollccollectors, orby the accidental closuretof onetor'more of the treadle contacts.

.-.I-n.-my Patent. No. 2,3l1,359; patented' February .16; 194:3, and assigned to the assignee of themesentiapplication,"there..isdisclosedea control system employing a multiple switch treadlejand. a

.group of electro-rmechanical relays actuated thereby :to operate ;counting devices only upon actuation x of the multiple switches in an overlapping sequence. The-relays employed with the control system disclosed in said-patent have an inherent inertia: and while adequatel-yresponsive iorvtoll checking, are prehaps limited in :trafiic ccountinginstallations to the relatively; moderate speed rangeof normal pleasure driving. It may 3150.136 said that. the maintenance andadjustment of-lmechanical relays requires amechanic of high skill and experience because such relays are relativelydelicate and precise tolerances of clearance :ofLthe-contacts-are usuallyessential to satisfactoryoperation. In otherthanlarge tollcollection installations, it =may be uneconomic to'have a skilled-mechanic in attendance, notwithstanding the fact that interruption of the functioning of ;.the;:apparatus for even a short time may result in confusion in the .count as well as loss of revenue.

The present invention utilizesa novel organization of thermionic tubes as switching means, in tlieutof the circuit-closing relays of 'thegprevious .s-ystem. llt is Well "known that ithermionic 1 tubes r are practically instantaneously responsive, and when employed as switching means have a speed range of response whichno vehicular speedcan defeat. Another desirable attribute of commercially available vacuum tubes is their high operating efficiency and trouble-free life expectancy, which materially exceeds that of the best of the mechanically actuated relays available for the purpose.

Generally speaking, it requires a .mechanic having a much higher degree .of skill to install or service a controlsystem embodying a multiplicity of mechanical relays,.than one basically involving vacuum tube circuits. Additionally,it is impossible topredict the-operating life or performance of a mechanical relay apparatus even after an inspection wherein all of the mechanical relays were apparently functioning properly.

In an installation embodying the present invention, the vacuum tubes and, the circuits thereof may be periodically inspected by a maintenance electrician :who mayhaveseveral installations under his care; and the characteristics of vacuum tubes are now so well-known that their useful life expectancy beyond the inspection day is predictable. At such periodic inspections, weak or doubtful tubes may be replacedat low cost-and barring accidental short circuits or damage to the electricity conductor system inherently present in any electrical installation-the satisfactory performance of the-control-system until the next inspection period may be-confidently expected.

The present invention may be installed inan existing system of treadle plates, and therefore the control system installation pursuant to-my said previous invention may be replaced by "a system as later described herein, with resultant material increase in the speed performance of the system. "The high speed response of a system embodying the present invention is of particular importance in installations on public highways, for example, where the objective may be to count vehicles, and the vehicles may be travellin at various speeds. from slow to high.

It is an object of the invention thereforexto provide a substantially trouble-free system for operation of a control or other electric device, responsive to sequential actuation of theswitches of a multiple treadle or the like.

It is yet another object of the invention to provide an improved system for operatingone .or more counters responsive to actuation of .a .mu-ltiple switch treadle substantially only b an object rolling thereover andxin-accordance with 3 the forward or reverse direction of movement of such object.

A further object of the invention is to provide an improved system for operating a counter or other electrical device upon passage of a vehicle wheel over a multiple switch treadle, said system being capable of operation over a broad range of vehicle speeds without loss of accuracy.

Still another object of the invention is to provide a control system for operating an electrical device responsive to actuation of a plurality of switches in overlapping sequence, and in which the continuous closing of one of the switches by mechanical or electrical failure or by other means will not prevent proper operation of the electrical device by sequential actuation of the remaining switches.

A further object of the invention is the provision of an improved electrical system for operation by a multiple switch actuator to provide an output impulse responsive to actuation of the switches in a progressive sequence in which at least two of the switches are actuated concurrently, with a momentary overlap of three switches.

Another object of the invention is to provide a control system for operating an electrical device by the actuation of a multiple unit switch according to a predetermined sequence of operation of groups of the switches of said unit.

A still further object of the invention is to provide a control system for actuating an electrical work circuit pursuant to the closing of groups of switches in a pre-established sequence, and to insure against actuation of said Work circuit by the operation of said switches in other than the predetermined sequence.

A further object of the invention is to provide means for indicating the number of times the switches of a multiple switch unit are closed in a predetermined sequence of operation of selected groups of said switches, and to disclose, b associated means, that groups of said switches are remaining in closed-circuit status for longer than a pre-established time period.

A further object of the invention is to provide means for the high speed counting of vehicles passing along a traflic lane.

Other features and advantages Will hereinafter appear.

Fig. l is a schematic wiring diagram of a four treadle thermionic control circuit embodying the present invention. Fig. 2 is the treadle circuit, only, of an embodiment of the invention employing a three-switch treadle. A suitable source of 220 volt direct current is presumed to be available. In the figure, the plus symbols represent 110- volts D. C. above ground; the minus symbols represent 110 volts below ground; and ground, therefore, may be considered as substantially at zero potential.

When the invention, as illustrated in Fig. 1, is employed as a traffic control system, or, for example, in a toll-collection station, there is disposed across the roadway, traific lane, or tollcollection lane, a multiple switch treadle T which has a series of contact plates A, B, C, D, arranged side by side and adapted to engage a common contact plate E individually when depressed as by the pressure of a vehicle wheel in rolling thereover. It will be understood that four separate plates may be used in lieu of the common plate E, so that the treadle may comprise four individual switches, if desired. Nevertheless, the four switches of the treadle T are 4 arranged closely side by side so that a vehicle wheel rolling over the treadle T will close the respective switches in an overlapping sequence in which at least two switches are closed concurrently, with a momentary overlap of three switches.

The treadle T may be made with the assembly of switches or plates suitabl insulated and disposed within a flexible envelope or housing. The plates A, B, C, and D are preferably of relatively narrow width and of considerable length, extending across a trafiic lane when the invention is used with road traffic. Said plates A, B, C, and D may be kept properly spaced laterally from each other and normally separated from plate E by suitable resilient separation strips or equivalent.

In the case of a wheel rolling from left to right, which is hereafter referred to as the forward direction, plate A will first contact with plate E, then plate B will contact with plate E, while A and E remain in contact, then plate C contacts with plate E, while A, B, and E are in contact. Plate D thereafter contacts with plate E, while B, C, and E remain in contact. All four plates need not be in contact with plate E concurrently, but sequential closure with a progressive overlap of closure of at least two is necessary for proper operation of the system described herein.

The function of the treadle switches is to provide means whereby the biasing potential in certain thermionic tubes may be regulated to control the periods of conduction and non-conduction of said tubes, as later described. There are numerous ways known to those skilled in the art for controlling the potential of a circuit; a simple and trouble-free method is by the use of resistance combinations.

Positive direct current is brought into a resistor l0, preferably 90,000 ohms, and then through conductor H to 200,000 ohm resistors l2, l3, l4, and I5 connected in parallel therewith. Said resistors are respectively in series with 5000 ohm resistors I6, [1, l8, l9, which connect to negative direct current. As appears, the respective plates A, B, C, and D are electrically connected to the four resistor circuits depending from the conductor ll, intermediate the respective resistor pairs l2-|6, I3l1, etc.

The resistors l6, l1, l8, and I9 serve to preload the respective treadle plates A, B, C, and D to compensate for possible leakage in the treadle and to insure an established or calculable operative result from the treadle circuits when a vehicle passes over the treadle plates.

Branching from the conductor l I is a conductor 20, in series with which is a one megohm resistor 2| in a grid circuit of one triode of a dual triode tube VT3 such as a standard 6SN'7 tube. The respective operating halves of said tube will be designated VT3a and VT3b. The resistor 2! is in the grid circuit of VT3a. The plate of VT3a is connected to positive potential through a 25,000 ohm resistor 22. From the said plate circuit extends a conductor 23, which serves two mutually symmetrical vacuum tube circuits designated F and R, which respectively operate the forward and re verse counter means, provide protection against erroneous counts resulting from roll backs, etc., as later to be described. Said circuits are connected to the said conductor 23 in parallel electrical relationship.

Triode VT3a of tube VT3 is the primary control element of the circuit. Until it is rendered consubstantially zero potential.

"ducting, the respective gaseous tubes VTl and which control'fiow ofpower for actuation of the counters'cannot be primed for actuation. Until it is returned to non-conducting condition,

the said tubes will not fire to operate the counter mechanisms which register forward or reverse travel of the vehicle across the treadle T.

When the respective treadle plates A, B, C, and D- are in their normally open position, conductor is at a high minus potential, pecause conductor l l connects to the high minus polarity of the systemthrough its respective branching circuits. The high minus potential maintains the grid of the triode VT3-a at minus potential, and the triode is therefore non-conducting, in which circumstance its plate and the therewith connected conductor 23, have positive polarity.

, Therconductor ll being connected to negative potentialthrough the four parallel circuits, any one of thetreadle plates may remain permanently closed with plate as might occur through jamming or like faulty operation, without raising the negative grid bias in the grid of tube VT3a suf- .ficiently to cause the tube to conduct.

Whentwoplates, such as A and B, are closed,

the current path in the two associated branch circuits isto ground through plates A and B and the common, grounded treadle plate E, and the potentialsin said branch circuits climb from the substantially minus 110 volt value to ground or The negative potentialinthe C and D branch circuits is insufficientto hold the potential in conductor 20 at minus and the grid of triode V'IBa goes sufiicient- .ly .positive'to cause the triode to conduct to ground. The potential in conductor 23 drops substantially to ground level.

VT3a exerts control over two circuits which collectively energize the output device or devices according to a sequential or coded actuation of the treadle switches. One circuit is a priming or primary circuit. In applications of the inven tion to trafiic counting systems, therernay be a forward travel and a reverse travelicounter,

respectively FC and RC, and there will be an F and an R priming circuit, respectively electrically connected to conductor 23 through. 23F and 23R. The secondary circuit is designated 23C,

and serves the output devices through the respective capacitors andiiiPt, as later appears. Referring now to the F circuit, a dual triode vacuum tube VTi, the respective triodes of which connects through grid is a branch comprising 400,000 ohm resistor 25 and a conductor 20 which connects to the plate.

circuit of VTlb. A second branch circuit connects to minus potential through the 800,000 ohm resistor 21. The plate circuits of VTIa and VTlb connect to positive potential through the respective 25,000 ohm resistors 23, 30.

- As is characteristic of such interconnected triodes, when one triode in the circuit is conducting, the other is non-conducting. With any three of the treadle plates open conductor 23 is at high plus potential. The grid of VTiais positive,'and the tube is conducting. With VT I b nonconductingits plate circuit is at high positive potential, increasing the plus bias'on thagrid of 1 When plates A.and B are closed with plate! E,

-tive-power from tube VT5b.

the potential in con'ductoriiZB :goes to ground, but the positive potential in conductor :26 keeps enough positive bias on the grid'of VTla, to keep the'tube'conducting; Conductor 29 is at ground potential, and thenegative potential exerted on the gridof VTlb through the two megohmresistor 01 holds triode VTlb non-conducting.

Attention isnow' directed to the second of the dual triode tubes in the F circuit, designated VT2. Its operating triodes are designated .VTZa and VT2b, respectively. It will be noted that the grid of VT2a connectsto positive power through the"? megohmresistor '32, and to the respective conductors 33 and '34 of the A and B treadle circuits through the.2'meg0hm resistor 35 and-the respective 200,000 ohm resistors 36 and 3?. When the treadle plates A or'Bare open, thegrid of VTZa isnegative because of the high negativeipotential of the-A 'and B treadle circuits, andthe tube is non con'ducting. When plates A andB are closed, conductors 33 and 34 go to ground potential, and the high plus bias exerted on the grid by its positive potential connectioncauses the'tube toconduct.

Circuits F and R are interlocked through a thermionic toggle switch inR which is identical with that of VTI. The dual triode tube of said circuit is designated VT5 and its respective triodes VT5a and VT5b. Before the closure of plates A and B, tube section VT5a was conductingand tube VT5b was non-conducting. It is noted that conductor '38 connects the plate of VTZa with the positive potential in the plate circuit of V'T5b and hence tube V'I2a receives posi- With tube VT2a conducting when the plates A and B are closed, the cathode of VT2a follows the grid to a positive potentiallevel. The cathode connects through conductor 39 and 200,000 ohm resistor 00 to conductor 41 and puts positive potential in said con ductor. With conductor 29 at ground, conductor 42 in the grid of VTlb goes positive, and tube VTIb conducts, reducing the potential in conductor 26 to ground. With both conductors 23 and 26 then at ground potential, the grid of VTla goes negative and the triode VT la is nonconducting.

The conductor 29 goes positive, and through one megohm resistor 43 maintains a plus grid bias on triode VTIb, holding it conducting.

In the described circuit, therefore, when the tube'VTlb is conducting, it signifies that the vehicle is travelling over the treadle in a forward direction. When the wheel of the vehicle continues to roll forward, it engages plates B and C before plate A is released; and the combination of the closed plates B and C maintains the circuits of VT3a and VTI in the same operative status as when plates A and B were closed.

WTZb, the other triode of VTZ has its plate circuit connect with the plate circuit of tube 'VTla through conductors 29, M, and 200,000 ohm resistor 45, and with VTla non-conducting, conductor 44 and the therewith associated plate of VT2b have a plus potential.

The grid of VTZb connects to positive power through conductor 46 and 400,000 ohm resistor 41; it also connects to the respective A and B treadle connections 33, 34, through conductor 48 and the respective 200,000 ohm resistors :39, The cathode of VTZb connects to ground. With A and B closed, tube VTZb becomes conducting to ground and tube VTla being non-conducting,

:conductor 44 has a-plus potential, but conductor 5| on the far side of the plate circuit of :tube

7 V'I2b is at ground potential. When A or B is opened, VTZb returns to non-conducting. With the momentary overlap of three plates, C will be closed when A or B is opened; VTla continues non-conducting and conductor goes to plus.

Conductor 51 connects to a voltage divider comprising one megohm resistor 52 and 600,000 ohm resistor 53, the latter connecting to negative potential through conductor 54. The grid of gaseous tube VT4 connects via 25,000 ohm resistor 55 and conductor 56, to the voltage divider. With ground potential at conductor 5|, there is a minus potential of about 70 volts on the grid of VT4. When A or B is opened and VT2b becomes non-conducting, the negative bias of the grid of VT4 is reduced to approximately 40 volts, priming the tube for firing.

A capacitor divider comprises .0005 mid. capacitor 51 and .0003 mid. capacitor 58, one side of each being connected to conductor 56.

Capacitor 5i connects to ground and capacitor 58 connects with conductor 23 through conductor 230, as shown.

When treadles A, B, and C are opened, tube VI3a reverts to non-conducting condition and hence conductor 23 goes rapidly positive. Capacitor divider 5?, 58 puts a plus surge in the grid circuit of gaseous tube VT4, sufficient to raise its grid bias and to fire the tube.

Thus the opening of treadles A and B, or either of them, primes tube VT4 for firing, and the opening of treadle C provides the necessary impulse for firing the tube.

VT4 is an 884, in which anything less than minus volts bias on the grid will fire the tube. A larger solenoid or other output device may require a higher capacity thyratron tube and other values in the capacitor divider, as known to those skilled in the art.

Tube VTd firing, it remains conducting through the solenoid FC, providing the current to draw the ratchet 50 thereof upwardly to rotate the number wheel 65 an amount sufficient to advance the counter one digit. A back contact 62, which is in series between ground, conductor 63, resistor 0 3 and the cathode of tube VT4 is operatively associated with ratchet 60, as by a lost-motion link 65. As the ratchet 60 completes its upward movement, contact 02 is opened, allowing the cathode potential to climb positively until the grid regains control and tube VT l extinguishes.

Capacitor El holds the plus potential on the cathode for a suiiicient time to insure complete deionization of the tube and for the potential and capacitor divider discussed above to restore to the approximately 70 volt bias. Current flow through solenoid FC ceases as the tube is extinguished and its ratchet moves downwardly under the urging of spring 66 to engage for the next counter operation.

The downward movement of the ratchet B0 ultimately closes the back contact 62, to bring the cathode of tube VT4 again to ground potential. The system is ready for the next forward count.

The reverse travel circuit R is a duplicate of the forward circuit, in the types of vacuum tubes and their respective positions in the circuit, and in the values of the respective resistors and capacitors associated therewith. A detailed description of the reverse circuit is believed unnecessary. It will be understood that the reverse travel of a vehicle across the treadle is from right to left, whereupon the order of actuation of the treadle plates is the reverse of that previously described.

Resistors and capacitors which are exact counterparts of those in the F circuit have been numbered as in the F circuit, with the addition of the letter R.

Tube VTG is the counterpart of VTZ, and the triodes VTfia and VTBb thereof perform the same function as the triodes WM and VTZb. VTBa is connected to plates C and D through the 2 megohm resistor 10, and the respective 200,000 ohm resistors l I, 12 and conductors 13, I4. VTGb is connected to plates 0 and D through the 200,000 ohm resistors l5, l6, and the respective conductors l3. 14.

The F and R circuits are interlocked by the conductor 1''? which connects from the plate circuit of VTlb to the plate of VTBa. The latter triode gets positive potential from the plate circuit of VTlb when triode VTlb is non-conducting status. Similarly as in VTZa, the cathode of V'IBa places a positive bias on the grid of triode VT5b which in turn biases triode VTEa to nonconducting status.

In the reverse travel, the closure of plates D and C makes the triode VT3a conduct, just as did the closure of the plates A and B in the forward direction of travel. Similarly, the closure of plates C and D causes the respective triodes VTGa and VT6b to become conducting, thereby impressing an approximately minus 70 volt potential on the grid of VTT, and the release of either plate C or D causes triode VTGb to become non-conducting to raise the negative bias on VTl to approximately 40 volts, priming the tube for firing.

The gaseous tube VT'I fires by reason of the plus surge introduced into the grid of tube VT'I through the capacitor divider 58R, 51R, as tube V'I3a becomes non-conducting, sending conductors 23, 23C rapidly to positive potential, following the opening of plate B as the wheel rolls across the treadle.

When VT! fires current flows through the reverse solenoid RC, through the tube, resistor 64R, conductor 63R, back contact 62R, to ground. As the ratchet 60R of reverse counter wheel 61R rises fully, the lost motion link 65R connecting the ratchet 60R and back contact 62R causes the said back contact to open to permit the cathode to go positive and to extinguish the tube, and halt current flow through solenoid RC, whereupon spring 66R resets the reverse counter for the next action.

It is apparent, therefore, that in either the forward or reverse travel of a vehicle across the treadle the operation depends upon having two plates closed concurrently, with a momentary overlap of three plates. The fourth plate in the treadle is a spare so that if any one of the others is held permanently closed, the operation of the system will be unafiected.

In the case of an axle counting system for toll checking the treadle is placed a short distance beyond the toll station so as that the car wheels will cross the treadle after toll is paid and the car moved forward in leaving the toll station. However, the restriction of the traific lanes at and near the toll station to permit cars passing around or crossing lanes extends for only a short distance and the treadles cannot be placed very far beyond the station. For this reason car drivers sometimes overrun the station somewhat and actuate the treadle in a forward direction and then back up to pay toll, again proceeding forward over the treadle after paying toll.

The present construction provides for this condltion by the count in both the reverse and forencased Ward: directions so that the forward countless the reverse count provides an accurate net forward-1 count.

Another. problem in toli check counting is *that thezfrontwheels of a can may, roll partway onto.

the treadle. Such a. conditionis sometimes also causedby the toll collector recalling th driver on account or an error in change or some. other question about the money or thedriver returns to, ask some question.-

It is: a feature of the present construction-that such rolling back andforth. will not interfere: with a correct net forward count.-

' Inasituation wherein a vehicleran forwardlyover the :treadle sufliciently only to; close. plates A and B with E, and then rolled back toopen either. A on-B, it is obvious thatithe-thyratron V'I'4 could not fire and there would be no forward, count.

If the Vehicle has rolled onto A, B, and. C,,

thenrolls in reverse; direction to open contact C.

only, the thyratron will not have primed, and;

could'not fire. If the vehiclerolls forwardly to the Band C combination, then rollsxbacktor-close Aa-ndB again, the thyratron, having been primed as the vehicle rolled forwardly, will deprime, and there willbe no actu-ationof the forward counter solenoid FC. The completion of the circuitfor actuating the counter-dependson a rolling forward over plates. A, B, and:C in succession, and.

a breaking-of the C plate connectionas well as a breaking oft-either theAorv Bsplate-connection.

The present inventionlprovidesfor indicating that'the treadle system or the circuits associated therewith have been tampered with 1 or operated insuch manner as to hold two or more of the:

treadlecircuits continuously closed-for afixed period of time: course, than the substantially momentary closure caused by a vehicle rolling over the treadle, evenv at a very low speed. A reasonable time limitof continuous, concurrent closure of twocontacts .or.

associated circuits has been arbitrarily established as five seconds. treadle plates are closed for more than five. secends, suitable signalling and/or recording means,

operates to indicate such prolonged closure.

The triode V'I3b operatesas a delayed switching means in anindicating. or recording circuit,

The grid of VTSZ) is connected to negative potential through the resistor 90, and its plate iscon- :1

nected to positive potential by a circuit which includes the relay coil 9|. A conductor 92;c0nnects to theconductor 23 from the plate circuit of triode VTSa, and thence, through-resistor 93 to the grid circuit of triode- V'ISb.

It will be recalled that. with'none, or only one of the plates A, B, C, or D closed with plate E, triode VTSa was non-conducting andthere was a positive potentialin conductor '23. This positive potential is also present in conductor 92, and.

is suflicient to positively bias the grid of V'I3b, so that the latter triode is normally conducting. The relay 9i is therefore energized and its. armature 94, which is connected to a source of current,

is held out of engagement with the contact. 95 which is in circuit with a lamp L,-'a printer PR'I or a bell BL. Hence, with triode VT3b conductlug, none of the illustratedsignalling or printing. ans will be energized.

W soon as two or more of the fourv treadle plates is closed withplate E, tube VT3a conducts and the potential in conductor 92 isreduced to round.

grid of VT3b, because of the condenser 96in the Said time period is longer, of

If two or more of the The reduction to ground potential in, conductor 92. isnot immediately; apparentin the.

ridcircuitg which, having a positive charge im-v pressed thereon while conductor 92 was positive. discharges when conductor 92 goes to g un diz laying-the reductiomto negative potential in the.

grid circuit of VT3b. Depending upon the capacity oftheicondenser and the values of the resisters 90,; 93, the reduction of the grid of =VT3ato sufficient ne-g-ativebias to stop the conducting action of triodeVIIT3bmay be delayed as desired.

Afteinthe time period has run, the grid of VTBb goes to negative, the triode ceases to conduct and the-relay- 94 is deenergized, permitting the armaturethereoi todropsout and to complete the circuitthrough the respective apparatus L, PH-T, BL,

to actuate the same and thus to signal that the.

system is being-tampered with or is. operating improperly,

It is frequently the practice in toll collection installations, to have a printer, such a-sPR'I',

,print ona tape at regularly established time intervals, such as every half hour or every hour,

If a supervisor, in examining the printedtape record, finds that the'apparatus has printing in termediatethe established times, it is an indicationthattheroperationof the treadle has either beenfaulty, or hasbeen tampered with, during suchperiod, andsteps may be taken to correct.

the error.

Fig. 2 discloses a circuit diagram, only. of a.

three treadle switch mechanism in which A and D are the sameas the similarly identified switches otFig: 1, and X is the-center switch which may beconsidered. as a combination of B and Cnof: In the three treadle circuit, the resistors. i2!,.l3 and [S eachhave one half *of the valueotthe-switches l2, l3, and I5; of Figure 1. The

Fig. 1.-

leads 33 and 14 connect with switches A and-D; just as; in.=the-Fig-. l circuit. The lead to thBjX switch of Fig. 2, is the combinationof' leads 34 and 13, inthe Fig. .1: circuit. In other words, when the three treadle circuit is employed, the respectively identified leads S it-and 13 are combined and brought to the Xswitch.

The; operation of the three; switch treadle is identical with that of the 'four switch system, ex,-

cept-thatnone-of the three switches may be held permanently closed. The safety factor of operat'ion:- characteristic of the four switch circuit is therefore absent in the Fig. 2 embodiment.

In recapitulation, it is seenthat the grid of the respective gaseous tubes VT4 and VT! is under thecontrolof vacuum tube switching means operating in a predetermined and controlled se-. quenceqby the concurrent closing of two switches of 1amultipl-e switch system, with a momentary overlap of; closing of atleast three of said switches.

Of the respective electronic tubes: VT4 constitutesz-aswitchiin the counter or other work circuit'; inthe appliactionof the invention described herein, said tube controls flow of power to the forward counter device;

tion... Additionally, VT! and VT5 reset the tubes,

of theactuating circuits when at least three vswitches. of afoul" switch system, or all ofa three VT'I is the reverse-direction counterpart of VT4L 4 11 switch treadle, are returned to open-circuit position.

WM and VTEa respectively select the proper counter circuit for forward and reverse travel indication.

VTZb and VTSb respectively prepare the priming grid bias for the respective forward and reverse counter actuating tubes VT4 and VTl.

There are four stages of control circuit operation for each actuation of the respective thyratron tube VT4 or VT'I.

Initially, that is, with at least three of the four switches of the Figure l embodiment open, or with all of the three switches of the Fig. 2 embodiment open, the control circuits are locked. Taking the F circuit as typical, VT4 is secured against operation by reason of the direct ground connection through VTla, which places ground potential in conductors 29, 44, and 5|. The high negative potential in conductor 54 therefore holds the grid of VT4 at high negative bias.

The second stage is preparatory, in which when plates A and B are closed, the path to ground at VTI a is interrupted, and positive potential is present in conductors 29, and 44. However, with switches A and B closed, tube VTZb becomes conducting to ground, and hence conductor 5! is at ground potential. The high negative in conductor 54 maintains the high bias on VT4.

Thirdly, there is a priming stage, which occurs when either switch A or B opens, whereupon VTZb is non-conducting, and conductor 5| goes positive. The voltage divider eiiect of resistors 52, 53 reduces the grid bias of VT4 to approximately 40 volts. The closure of switches B and C, or C and D, maintains tube VT3a conducting to ground.

During the two stages immediately above, the thermionic toggle interconnection of the tubes VTla and VTlb maintains VTla in non-conducting condition.

The final or firing stage occurs when switch C is opened during continuing movement of the vehicle in one direction. Tube VT3 reverts to nonconducting and a plus surge from the switch circuit of VT3a is impressed upon the capacitor 58, resulting in a strong plus surge in the grid circuit of VT4 suificient to cause the tube to conduct and hence to energize the counter or indicator. In the interim immediately following the opening of switch C, tubes VTIa and VTIb have toggled to their original operative statusthat is, their operating condition before the vehicle began travel across the treadle-but the delaying action of the several resistors in the F circuit restrains the return of the high bias condition of VT4 until after the positive surge has occurred across capacitor 58. As is well-known, when an electronic tube of the thyratron type commences to fire, the grid alone is ineifective to gain control over the tube to extinguish it. In order to extinguish tube VT4 and to restore the entire circuit to its original locked position, the cathode of VT4 is permitted to climb in a positive direction by disconnecting the cathode from ground, through the delayed opening of the back contact 62. As the cathode connection to ground is opened, the climbing cathode extinguishes the tube to permit the grid thereof to resume control; the circuit is ready for the next operation.

It will be recalled that the plate of tube VTZa derives positive power from the plate circuit of Will) through conductor 38, and that the plate of tube VTBa derives positive power from the plate circuit of VT), through conductor 11.

12 When switch plates A and B are closed, tube VAZa became conducting and current flowed through conductors 38, 39, 4!, and 42 to the grid of VTlb causing VTlb to become conducting and to toggle VTla into non-conducting condition.

As switches A and B, or either of them, are opened, VT2a returns to non-conducting, but there is enough plus reaction through conductor 29 and resistor 43 to hold conductor 42 willciently plus to maintain VTlb in conducting status. The closure of switches C and D by the vehicle passing thereover brings the grid of VTGa to conducting bias, but since VTlb is continuing to conduct to ground, there is ground potential in conductor 11 and tube VTGa is locked in nonconducting condition.

If the A and B treadle switches are the first to close, therefore, VT5a cannot be toggled to non-conducting condition, and the R circuit is locked against operation of its associated thyratron VT'l.

For vehicles travelling in the reverse direction, the closure of switches D and C would initiate operation of the R circuit and the F circuit would be locked against operation of thyratron VT4.

Therefore, it is apparent that the operation of the F or R control circuits depends upon which of the pairs of switches AB, or DC, is first closed by the vehicle in passing over the treadle.

In the foregoing description, and in the claims, the expressions conducting and non-conducting are used in describing the operative status of the respective vacuum tubes. A conducting tube is considered to be one in which the grid bias permits substantial current flow between the plate and cathode of the tube; a non-conducting tube has a grid bias which prevents such flow.

It will be understood that the circuit specifically disclosed herein, and the constants and values ascribed to the disclosed resistors and capacitors, are not recited in a limiting sense, but are illustrative of a circuit which satisfactorily performs the features and objectives of the invention.

Whereas it is obvious that the several objects of the invention as specifically afore noted are achieved, it is apparent that numerous changes in construction and rearrangements of the elements might be resorted to without departing from the spirit of the invention as defined by the claims.

I claim:

1. Means for counting vehicles proceeding along a trafiic lane, including a switch unit having at least three switches so spaced that a vehicle wheel travelling thereover in a continuing direction will close two switches simultaneously, with momentary overlapping closure of three; an electrically energized counter; an electrically potentialized circuit connected therewith for actuating the same, and means for establishing, in stages, a priming potential and an actuating potential in said circuit; said means including vacuum tube toggle switching means electrically in circuit with said switches and normally stable, with any two of said switches open, to connect said actuator circuit to ground by vacuum tube conduction and having a second condition of stable equilibrium to interrupt said ground connection when any two of said switches are closed; vacuum tube means electrically in circuit with all three of said switches and with said toggle switching means to prepare the latter for transition to said second condition of equilibrium so long as any two of said switches are closed; a second vacuum tube means electrically in circuit with the two switches first closed by a vehicle in passing over said switch unit and accuses;

incircuit with' said toggle switching means toxbiasthe latter to itssaid secondposition of equilibrium as -said .two switches are closed; at third. vacuum tubesmeans electricallylin'circuit with-said. firstclosed" two switches for restoring connection be tween said actuatorcircuit and ground by vacuum tube conduction as Said two switches are closed and'interruptin said ground connection aszone:

oi said? two switches is openedduring travelof the-vehicle over said switch unit; voltage, divider nieansin said actuator circuit to maintain a;

counter non-operating potential therein while saidicircuit is grounded and upon interruption of said ground connection to prime the potential inzsaid' circuit to a value and "polarity approaching'a'th;

means, a'the-rmionic tube for controlling current flowto said counting means, and a potentialized control circuit forthegrid of-said tube forestablishi'ng a grid bias thereof for actuation of said counting meansupon coded closure of said switch means; comprising in said grid circuit apair of vacuum'tubes interconnected in togg-lecircuit relationship; one-of the saidvacuum tubes arrangedtoconnect said grid control circuit/to ground by'vacuum tube conduction; a secondvacuum tube electrically in circuit with said three switches and-with said toggle-connected vacuum tubes to establish the ground; connection of the grid con-- trolicircuit when said switches are inopen-circuit position and to prepare said toggle switching means for interruption of said connection to ground upon closure of two of'said switches; a

third vacuum tube m ans electrically in circuit with the first two of said switches toclose upon travel of a vehicle thereover and in circuit with said'toggle-connected tubes to bias the'said groundconducting tube to non-conducting status upon closure of said two switches; a fourth vacuum tubenieans in saidcontrol circuit for-establishing a secondground connection'therefor by vacuum tube conduction upon closure of said firsteclosed two switches and interrupting said connection uponreturn of either of said two switches to open condition; voltage divider means in said control circuit and effective while the control circuit" is grounded to place a high'bias on the gridofsaid thermionic tube and upon interruption of said ground connection bring said grid nearly to a threshold level of thermionic tube conduction; and'means electrically in circuit with said second named vacuum tube and with said grid control circuit to momentarily impress additional potential in said grid control circuit to carry the grid over the threshold level of operation of said tube as the third of said switches is opened;

3. Means for indicating direction of travel of a vehicle along. a traflic lane, comprising a for ward travel indicator; a reverse travel indicator;

an electrically potentialized; actuator circuit in-, dividual to each said indicator for actuating the (ill 14' same; and means for energizingaselected actuatorcircuit to establish, inestages, a priming potential andan' operating-potential to actuate the indicator thereof, including in each actuator circuit vacuumtube-toggle switching means-having a-condition' of stable equilibrium connecting said circuit'toground Icy-vacuum tube conduction andra: second-condition in which the ground connection is interrupted; a switch unit including at least three-.- normally open switches disposed in said itrafile lane in'such spaced relationship that HIV-61110161 wheel, travelling thereover in a continuing direction will close-said switches in groups of? two with; momentary overlapping closure of three: switches; vacuum tube means controlled byjsaidiswitchunit and connected to each said actuator circuit to lock the toggle switchingmeans thereof in circuitgrounded condition when thegswitches of'saidrunit are open and upon c10s-- ing-zany' twoof said'switches to unlock the toggle switching'means for'toggling to the other 001M111- tionlof equilibrium; vacuum tube means for the forward-travel actuator circuit connected to the toggle switching means thereof and in circuit withwthe pairv of switches first closed by a for-- ward travelling vehicle; vacuum tube means similarly connected in the'reverse-travel circuit and? in circuit with the pair of switches first closed by a reverse-trave1ling vehicle, the closure ofv one of said pairs ofswitches biasing its associated last-namedvacuum tube means into conducting-condition to actuate its associated toggle switchto' ground disconnect condition; means for holding the toggle switch-of the other circuit in ground connect status, further vacuumtube meansineach actuator circuit and respectively controlled by the forward-travel switch pair and the reverse-travel switch pair, said further vacuum tube means being operative to restore its associated ground-interrupted actuator circuit: to ground connection by vacuum tube conduction upon closure of its associated two switches andtodnterrupt the path to ground upon the return oi'one of'said'switches toopen condition as'the vehicle continues its travel; voltage divider means in each said circuit effective upon the final ground disconnect condition of the forward or reverse actuator circuit to establish therein a preparatory value and polarity of potential approaching a threshold value for operating the indicator of said circuit; means in said actuator circuit and deriving power from the first-named '7 circuitto above said threshold level for actuation of said indicator.

4; Means for indicating direction of travel of a vehicle along a trafiic lane, comprising a forward travel indicator; a reverse travel indicator; an actuator circuit-individualto each indicator for actuating'the same; a source of positive potential and a" source of negative potential connected to each said'actuatorcircuit; and means for establishing a potential in said'circuits suflicient to actuate its associated indicator according to direction of vehicle travel; including: in each actuator circuit a pair of vacuum tubes interconnected toprovide vacuum tube toggle switching means having a condition of stable equilibrium in which thepositive potential in the associated actuator circuit is neutralized by vacuum tube conduction to'groundjand a second condition of equilibrium in'which said ground'connection is interrupted; a switch unit including a plurality of'normally open switches disposed in said traffic lane and arranged to be closed in grounps of two switches with momentary overlapping closure of three switches by a vehicle travelling thereover in a continuing direction; electric potential means in circuit wi h said switch unit and with each of said pairs of vacuum tube toggle switching means to bias the same in ground connection condition thereof when the switches of said unit are in open circuit position and to reduce the bias to prepare said toggle switching means to toggle to their other condition of equilibrium upon closure of any two of switches by a vehicle travelling over said switch unit; a second vacuum tube means in each actuator circuit and respectively in circui'; 'l energized by the two switches first closer by a vehicle traversing said switch imit in a forward or reverse direction, said latter vacuum tube means of each actuator circuit being in circuit with the toggle switching means of its actuator circuit to bias said means to toggle to ground-interrupt condition according to which pair of switches is first closed by said vehicle, the vacuum tube means associated with such first closed two switches deriving its biasing potential from an element of the toggle switching means of the other actuator circuit to hold said latter toggle switching means at ground-connect status; further vacuum tube means in each of the two actuator circuits in advance of the negative potential source thereof, each said latter vacuum tube means being respectively controlled by the first two switches closed by a vehicle travelling in a forward or reverse direction and adapted to restore the ground connection of its associated actuated circuit upon closure of the said two switches and to interrupt the ground connection upon the return of one of said two switches to open condition as the vehicle continues its initial direction of travel; voltage divider means electrically connected between the respective sources of positive and negative potential to establish a potential in the actuator circuit approaching the threshold level of actuation of the indicator as the last named connection to ground thereof is interrupted, and means deriving power from the electric potential means in circuit with said switch unit for momentarily carrying the potential in said actuator circuit above the threshold level to actuate the associated direction indicator as a third switch of said switch unit is opened as the vehicle continues its travel over the switch limit of operating potential, and means for controllably establishing said operating potential, comprising a priming circuit having a normal potential which is less than such operating potential, and a supplemental circuit capable of momentarily impressing additional potential to additively equal or exceed such operating potentlnl: said priming circuit including a thermionic t gle switch having a condition of stable equilibrium bypassing said circuit to depress the normal potential thereof and a second condition interrupting said bypass; a normally non-conducting vacuum tube in said priming circuit for establishing a second potential-depressing bypass by vacuum tube conduction; a biasing circuit common to said toggle switch and said vacuum tube and having a potential normally biasing said toggle switch to its first condition of equilibrium and said vacuum tube to non-conducting status;

vehicle actuated means for changing the potential in said biasing circuit to throw said toggle switch to its said second condition and simultaneously to bias said vacuum tube to conducting status; a second biasing circuit including a second vehicle-actuated means actuated sequentially after the first-named means for holding said toggle switch in its second equilibrium condition while the return of said first-named vehicle actuated means to initial status restores said vacuum tube to non-conducting status to establish the normal potential of said priming circuit; and means electrically connecting said last-named vehicle actuated means and said supplemental circuit and responsive to return to initial status of said last-named vehicle actuated means to momentarily potentialize said supplemental circuit to increase the potential in said counting means sufficiently to operate the same.

6. A traffic counting system according to claim in which said supplemental circuit includes capacitor means charged during actuation of said second-named vehicle actuated means and discharging into said counting means upon restoration of said vehicle actuated means to initial status.

'7. A traiilc counter, including electrically energized counting means; a normally non-conducting gaseous thermionic tube in the electrical circuit of said counting means and adapted to energize said counting means when said tube is conducting; a vehicle-actuated treadle embodying a plurality of switches for sequential actuation by a Vehicle wheel rolling over the treadle in a continuing direction; and an electric circuit in the grid circuit of said thermionic tube and controlled by the said switches, said circuit including electronic switching means connecting the grid of said thermionic tube to a high negative potential as certain of said switches are actuated by said vehicle wheel, voltage divider means effective upon the release of one of said switches and the actuation of another switch to reduce the grid bias of said thermionic tube; and further electronic switching means electrically connected to said switches and including a capacitor divider in the grid circuit of said thermionic tube and said last named means being efiective upon the release of said last-named switch to place a plus surge on the grid of said tube sufficient to cause the same to become conducting.

8. Means for counting the passage of vehicles along a trafiic lane, comprising a switch unit of at least three switches disposed at a fixed location in said traffic lane in such spaced relationship that a vehicle passing said location will sequentially actuate said switches with momentary overlapping actuation thereof; an electrically energized counting means; a control circuit for said counting means, including potential divider means for providing an electrical potential of slightly less than energizing level of said counting means upon the actuation of two of said switches and the return to initial status of one of said two switches as a vehicle passes thereover; a second control circuit responsive to the concurrent actuation of a second and third of said switches to cause the first-named control circuit to maintain such electric potential; and means electrically associating said second control circuit and said c unting means to increase the electrical potential at said counting means to a value suificient to energize the same as all of the said three switches return to normal status as the vehicle proceeds beyond the switch unit.

9. A vehicle-operated system for actuating electrically energized counting means, comprising a gaseous triode functioning as a normally nonconducting element in series in the circuit of said counting means; a grid control circuit for said triode; a plurality of electric switches adapted upon passage of a vehicle thereover to be sequentially closed with momentary overlapping closure of all switches; means responsive to the closing of certain of said plurality of switches to impress a high negative bias on the said grid circuit to prevent conduction in said tube; means responsive to the subsequent opening of at least one of said switches and the simultaneous closing of another switch to reduce the grid bias from such high negative value to a point approaching but not attaining a level suificient to cause said triode to become conducting, means responsive to the opening of said last-named switch while keeping at least one of said first-named switches open to further reduce the grid bias of said triode from such point to a level at which said triode becomes conducting in said work circuit and said counting means is actuated; a switch operatively associated with said counting means and normally connecting the cathode of said triode to relatively low potential; and means responsive to operation of said counting means to open said switch to permit the cathode to climb positively to a potential at which the grid of said triode regains control thereover.

10. A system for controlling an electric work circuit, comprising a gaseous triode functioning as a normally non-conducting element in series with said work circuit; a grid control circuit for said triode; a plurality of electric switches arranged for sequential operation, with momentary concurrent operation of all switches; a source of positive and a source of negative potential for said control circuit; means responsive to the closing of a group of said plurality of switches to bypass the positive potential of said control circuit to permit the negative'potential to impress a high negative bias in the grid circuit of said triode to prevent conduction therein; means responsive to the subsequent opening of at least one of said group of switches and the simultaneous closing of another switch to supersede such high negative bias and to establish the grid bias at a point approaching but not attaining a level sufiicient to cause said triode to become conducting; means responsive to the opening of said last-named switch while keeping at least one of said first-' named switches open to shift the grid bias of said triode from such point to a level at which said triode becomes conducting; and means effective consequent to the conducting condition of said triode to permit the grid of the triode to regain control thereover.

11. In a vehicle actuated counting system, a switch unit disposed in a traflic lane and having a plurality of switches so disposed that a vehicle travelling thereover closes said switches in sequence, with momentary overlapping closure of all; a counting means responsive to coded closure of said switches by a vehicle in travelling in one direction over said switch unit; a second counting means responsive to coded closure of said switches by a vehicle in travelling in the opposite direction, and means for selectively actuating the counting means according to direction of travel, including a control circuit for each said counting means; a double triode thermionic toggle in each said counting means circuit and normally in a condition of equilibrium holding its associated counting means circuit at non-operating potential when all of said switches are open; vacuum tube means electrically associated with said switches and a triode of each said thermionic toggle to prepare each said toggle upon closure of any two of said switches to assume a condition of equilibrium in which each said counting means circuit may be supplied with operating potential; and a third vacuum tube means in each said counting means circuit and respectively electrically connected to those two switches first closed by a vehicle travelling over said switches in one or the other direction and with the toggle of said circuit to throw the toggle to its said second condition of equilibrium upon the closure of the said two switches, each said last-named vacuum tube means deriving its operating potential from a triode of the toggle of the opposite counting means circuit.

12. In a vehicle actuated counting system having counting means respectively responsive to forward or reverse travel of a vehicle, means for selectively actuating said counting means, including a switch unit having at least three normally open switches so disposed in a trafiic lane that a vehicle passing thereover closes said switches in groups of two with momentary overlapping closure of three switches; an electric circuit for each said counting means, and each circuit being electrically controlled by a different group of two of said switches; a thermionic toggle switch in each said circuit and having one condition of equilibrium in which the respective circuits are held at a potential precluding operation of its associated counting means and a second condition of equilibrium wherein the respective circuits may be brought to operating potential, vacuum tube means actuated by the closure of any two of said three switches and connected to each said thermionic toggle switch to prepare each for transition to its second condition of equilibrium upon closure of any two of said switches; and means in each of said counting means circuits and electrically associated with the toggle switch thereof, said means controlling a source of electrical potential and responsive only to the closure of the group of two switches associated with its said counting means circuit to impress said potential on the associated toggle switch to cause said toggle switch to assume its said second condition of equilibrium, said potential being derived from an element of the toggle switch of the opposite counting means circuit.

13. In a system for counting the number of vehicles passing along a trafiic lane, a switch unit disposed in said lane and comprising a plurality of switches so arranged that a vehicle wheel rolling over said unit will close said switches in sequence; means for counting the number of vehicles passing over said switch unit in one direction; a second means for counting the number of vehicles passing over said switch unit in the opposite direction; control circuits for each said counting means; vacuum tube means having its plate circuit in parallel with each of said control circuits, said vacuum tube means being controlled by said switches to conduct from positive potential to ground with certain of said switches in closed circuit position and being non-conducting to ground with said switches in open circuit position; and means for indicating a prolonged closure of said switches, comprising indicating means, a magnetic switch for controllin said indicating means, a second vacuum tube means having its grid biased to conducting potential by the plate potential of said first-named vacuum tube means when the latter is in non-conducting status, said second vacuum tube means, when conducting, actuating said magnetic switch for non-operation of said indicator; and time delay means in the grid circuit of said second vacuum tube means to impress a non-conducting bias on the grid thereof at a predetermined period of time after the firstnamed vacuum tube becomes conducting upon closure of said two switches; a non-conducting condition of said second vacuum tube actuating said magnetic switch to close the circuit to said indicator.

14. In a system for counting the passage of vehicles along a trafiic lane, a switch unit disposed in said trafiic lane and comprising a plurality of switches so arranged that a vehicle rolling over said unit will close said switches in sequence; an indicator and control circuit therefor; a relay in said control circuit; and vacuum tube means in circuit with said relay and energizing the same for holding said indicator circuit open while said vacuum tube means is conducting and deenergizing said relay to close said indicator circuit when said tube means is non-conducting; a biasing potential for the grid circuit of said vacuum tube; means operating with said switches in open circuit position to bias said grid to conducting condition and with certain of said switches in closed position to bias said grid to non-conducting condition; and means for delaying the transition from conducting to nonconducting condition of said grid following closure of said switches.

15. In a system for counting the passage of vehicles along a traffic lane, a switch unit disposed in said traffic lane and comprising a plurality of switches so arranged that a vehicle rolling over said unit will close said switches in sequence; an indicator and control circuit therefor; a relay in said control circuit; and vacuum tube means in circuit with said relay and energizing the same for holding said indicator circuit open while said vacuum tube means is conducting and deenergizing said relay to close said indicator circuit when said tube means is nonconducting; a biasing potential for the grid circuit of said vacuum tube; means operating with said switches in open circuit position to bias said grid to conducting condition and with certain of said switches in closed position to bias said grid to non-conducting condition; and a resistor and capacitor circuit in said grid circuit for delaying the transition from conducting to non-conducting condition of said grid following closure of said switches.

16. In a traflic counting system including counting means, switch means in a roadway and embodying a plurality of switches for momentary overlapping closure by passage of a vehicle wheel thereover and means whereby such momentary closure prepares said counting means for actuation, means for indicating a prolonged closure of said switches, comprising an indicator, an electric circuit therefor, vacuum tube means in said circuit to control current flow therethrough, a grid control circuit for said vacuum tube electrically in circuit with said switches, electrical potential means in circuit with said switches and said grid circuit to bias the grid of said tube for vacuum tube conduction when said switches are open and to bias said tube to cut off upon closure of said switches, said grid control circuit having resistance and capacitance means to delay the impression of cutofi bias on said tube for a predetermined time period after closure of said switches; and means responsive to the cutofi of said vacuum tube to operate the indicator.

1'7. An electrical network for energizing an out.- put device having an established lower limit of o erating potential, comprising a first and second energizing circuit connected to the input of said device, each said circuit being potentialized to supply to the device a potential which is less than its operating potential, but additive to the required value; a first and second vacuum tube means in a first of said energizing circuits, each being in an electric circuit bypassing said output device by vacuum tube conduction to neutralize the potential in said circuit; biasing circuits for said vacuum tube means normally po-' tentialized to maintain said first tube conducting and the other non-conducting; control means common to said biasing circuits for altering the biasing potential thereof to reverse the operating status of the respective vacuum tube means upon actuation of said control means; a second control means for the biasing circuit of said first vacuum tube means for actuation following actuation of said first-named control means to hold said first vacuum tube means non-conducting as the return to normal status of said first control means reestablishes the potential in its biasing circuit to return the second vacuum tube means to non-conducting status; the second energizing circuit being electrically in circuit with said second control means and responsive to the return to normal status thereof to impress a potential upon the output device sufficient to supplement the potential of said first energizing circuit to operate the output device.

18. An electrical network for energizing an output device only by a predetermined sequential operation of a plurality of switches, comprising a partially energizing circuit for said output device, said circuit being capable of supplying to said device an electrical potential which approaches but does not attain the threshold level of potential for actuating said device; means in said circuit and electrically in circuit with cer tain of said switches for depressing the potential of said circuit below said threshold approach potential when said switches are in open circuit status andfor removing the last mentioned depressant efiect with said certain switches in closed circuit status; means in circuit with another of said plurality of switches and connected with said depressant means to hold said means in depressant-removing condition upon closure of said second named switches in overlapping relationship with closure of said first switches and subsequent opening of one of said first switches; means in partially energizing circuit for momentarily delaying the return of said depressant means to original open circuit status uponopening of all of said switches; and electric circuit means in circuit with the last of said switches and with said output device, and responsive to the opening of said switches to place a momentary additional surge of potential in said output device sulficient to supplement said partially energizing circuit in such depressant removing condition to carry beyond the threshold value of operation potential of said output device to actuate the same.

19. A system for the control of an electric work circuit, comprising a thermionic tube in said work'circuit and adapted to function as control means therein; a grid control circuit for said thermionic tube; a multiple switch unit; means for impressing on said thermionic tube a grid bias of substantially fixed value suificient to prevent substantial current flow in said tube upon closing a selected group of switches in said mul-- tiple switch unit; means for reducing said grid bias to a point intermediate such fixed value and a current flow permitting value upon opening certain of said group of switches after such preceding closure; and means responsive to the subsequent opening of additional switches of said group further to reduce the grid bias of said thermionic tube from such intermediate point to permit current flow therein.

20. A system for the control of an electric work circuit, comprising a thermionic tube in said work circuit; means for connecting a plurality of switches for subsequent operation to control the grid circuit of said thermionic tube; said last means including means for impressing a predetermined grid bias sufficient to prevent conduction on said thermionic tube upon the closing of at least an initial two of said switches, means for reducing the said bias from such predetermined bias to a level approaching the threshold level for conduction of said tube upon the subsequent opening of at least one of said two switches while simultaneously closing a third switch of said multiple switch unit, and means resulting from the opening of said third switch while at least one of the first-named switches remains open, to potentialize said grid from said approach level to beyond the threshold level to bring said tube to conducting status, and means responsive to said conducting status to energize said work circuit.

21. A system for controlling an electric work circuit comprising a gaseous triode functioning as a normally non-conducting element in series with the said work circuit; a grid control circuit for said triode; a plurality of electric switches; means responsive to the closing of at least an initial two of said plurality of switches to impress a high negative bias on the said grid circuit; means responsive to the subsequent opening of at least one of said switches and the simultaneous closing of a third switch to reduce the grid bias to a point approaching, but not attaining, a threshold level for conducting condition of said triode; means responsive to the opening of said third switch while keeping at least one of said firstnamed switches open to carry the grid bias from such approach point to beyond the threshold level; and means independent of said switches and energized by the conducting status of said triode, to restore said triode to non-conducting condition.

JOHN L. BARKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,205,555 Cooper June 25, 1940 2,311,359 Barker Feb. 16, 1943 2,313,627 Cooper Mar. 9, 1943 

